Vehicle washing systems typically comprise a combination of top and side brushes to contact and scrub all of the exterior surfaces of the vehicle as effectively as possible. In a typical arrangement the front surfaces of the vehicle are washed by one or more brushes having vertical axes of rotation and vertical pivot axes located to the sides of a wash lane. The brushes themselves stand in the path of the vehicle and are pushed through their angular range of travel by engagement with the vehicle. The brushes thereafter pass along the sides of the vehicle. A top brush, having a horizontal axis of rotation, is typically mounted with the pivot axis nearest the approaching vehicle so as to intercept the hood or windshield of the vehicle and be pushed up and over the vehicle as further relative motion occurs. This top brush is relatively incapable of washing the rearmost surfaces and particularly the lower, rearmost surfaces of the vehicle, because the brush is not permitted to fall to its lowermost position until the vehicle clears the brush and at this point the angular trajectory of the brush carries it away from the vehicle.
As a result, it is common to see personnel stationed near the entrance of a car washing establishment with brushes and buckets of soapy water for the purpose of manually washing down the rear surfaces and particularly the lowermost rear surfaces of the entering vehicles.
One approach to eliminating this need for a manual washing function is disclosed in U.S. Pat. No. 3,939,517 issued Feb. 4, 1976, to the present inventor. In that patent a horizontal brush is supported by an articulated frame the end portion of which can be pivotally extended forward in such a fashion as to reach out and scrub the rear surfaces of a receding vehicle. In addition, the horizontal brush may be shifted laterally to provide an additional scrubbing function. Although extremely effective, this approach does add to the technical complexity and cost of the system.
Another approach is described in U.S. Pat. No. 3,798,696 issued Mar. 26, 1974, to John F. Cirino. In this patent the horizontal brush is mounted on a pair of pivot arms with the pivot axis farthest from the approaching vehicle and with the brush extending toward the approaching vehicle. In this arrangement, the brush may pass downwardly over the rear window, deck, and lower rear surfaces of the vehicle, the angular path of travel being toward rather than away from the vehicle so as to permit contact to be maintained. It is recognized by the inventor that because the horizontal brush includes an axially symmetrical counterweight, the component of force tending to urge the brush against the vehicle diminishes to the point of negligibility toward the lowermost end of the angular path of brush travel. As a result, the system comprises an apparatus for manually applying additional force to the brush tending to maintain it in engagement with the vehicle at the lower end of its path.